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package java.security.spec;

import java.util.Objects;

/**
 * This class specifies a parameter spec for RSASSA-PSS signature scheme,
 * as defined in the
 * <a href="https://tools.ietf.org/rfc/rfc8017.txt">PKCS#1 v2.2</a> standard.
 *
 * <p>Its ASN.1 definition in PKCS#1 standard is described below:
 * <pre>
 * RSASSA-PSS-params ::= SEQUENCE {
 *   hashAlgorithm      [0] HashAlgorithm      DEFAULT sha1,
 *   maskGenAlgorithm   [1] MaskGenAlgorithm   DEFAULT mgf1SHA1,
 *   saltLength         [2] INTEGER            DEFAULT 20,
 *   trailerField       [3] TrailerField       DEFAULT trailerFieldBC(1)
 * }
 * </pre>
 * where
 * <pre>
 * HashAlgorithm ::= AlgorithmIdentifier {
 *   {OAEP-PSSDigestAlgorithms}
 * }
 * MaskGenAlgorithm ::= AlgorithmIdentifier { {PKCS1MGFAlgorithms} }
 * TrailerField ::= INTEGER { trailerFieldBC(1) }
 *
 * OAEP-PSSDigestAlgorithms    ALGORITHM-IDENTIFIER ::= {
 *   { OID id-sha1       PARAMETERS NULL }|
 *   { OID id-sha224     PARAMETERS NULL }|
 *   { OID id-sha256     PARAMETERS NULL }|
 *   { OID id-sha384     PARAMETERS NULL }|
 *   { OID id-sha512     PARAMETERS NULL }|
 *   { OID id-sha512-224 PARAMETERS NULL }|
 *   { OID id-sha512-256 PARAMETERS NULL },
 *   ...  -- Allows for future expansion --
 * }
 * PKCS1MGFAlgorithms    ALGORITHM-IDENTIFIER ::= {
 *   { OID id-mgf1 PARAMETERS HashAlgorithm },
 *   ...  -- Allows for future expansion --
 * }
 * </pre>
 * <p>Note: the PSSParameterSpec.DEFAULT uses the following:
 *     message digest  -- "SHA-1"
 *     mask generation function (mgf) -- "MGF1"
 *     parameters for mgf -- MGF1ParameterSpec.SHA1
 *     SaltLength   -- 20
 *     TrailerField -- 1
 *
 * @see MGF1ParameterSpec
 * @see AlgorithmParameterSpec
 * @see java.security.Signature
 *
 * @author Valerie Peng
 *
 *
 * @since 1.4
 */

public class PSSParameterSpec implements AlgorithmParameterSpec {

    private final String mdName;

    private final String mgfName;

    private final AlgorithmParameterSpec mgfSpec;

    private final int saltLen;

    private final int trailerField;

    /**
     * The {@code TrailerFieldBC} constant as defined in PKCS#1
     *
     * @apiNote This field is defined in Java SE 8 Maintenance Release 3.
     * @since 8
     */
    public static final int TRAILER_FIELD_BC = 1;

    /**
     * The PSS parameter set with all default values
     *
     * @since 1.5
     */
    public static final PSSParameterSpec DEFAULT = new PSSParameterSpec
        ("SHA-1", "MGF1", MGF1ParameterSpec.SHA1, 20, TRAILER_FIELD_BC);


    // disallowed
    private PSSParameterSpec() {
        throw new RuntimeException("default constructor not allowed");
    }


    /**
     * Creates a new {@code PSSParameterSpec} as defined in
     * the PKCS #1 standard using the specified message digest,
     * mask generation function, parameters for mask generation
     * function, salt length, and trailer field values.
     *
     * @param mdName       the algorithm name of the hash function
     * @param mgfName      the algorithm name of the mask generation function
     * @param mgfSpec      the parameters for the mask generation function.
     *         If null is specified, null will be returned by
     *         getMGFParameters().
     * @param saltLen      the length of salt
     * @param trailerField the value of the trailer field
     * @exception NullPointerException if {@code mdName}, or {@code mgfName}
     *         is null
     * @exception IllegalArgumentException if {@code saltLen} or
     *         {@code trailerField} is less than 0
     * @since 1.5
     */
    public PSSParameterSpec(String mdName, String mgfName,
            AlgorithmParameterSpec mgfSpec, int saltLen, int trailerField) {
        Objects.requireNonNull(mdName, "digest algorithm is null");
        Objects.requireNonNull(mgfName,
            "mask generation function algorithm is null");
        if (saltLen < 0) {
            throw new IllegalArgumentException("negative saltLen value: " +
                                               saltLen);
        }
        if (trailerField < 0) {
            throw new IllegalArgumentException("negative trailerField: " +
                                               trailerField);
        }
        this.mdName = mdName;
        this.mgfName = mgfName;
        this.mgfSpec = mgfSpec;
        this.saltLen = saltLen;
        this.trailerField = trailerField;
    }

    /**
     * Creates a new {@code PSSParameterSpec}
     * using the specified salt length and other default values as
     * defined in PKCS#1.
     *
     * @param saltLen the length of salt in bytes to be used in PKCS#1
     *         PSS encoding
     * @exception IllegalArgumentException if {@code saltLen} is
     *         less than 0
     */
    public PSSParameterSpec(int saltLen) {
        this("SHA-1", "MGF1", MGF1ParameterSpec.SHA1, saltLen, TRAILER_FIELD_BC);
    }

    /**
     * Returns the message digest algorithm name.
     *
     * @return the message digest algorithm name
     * @since 1.5
     */
    public String getDigestAlgorithm() {
        return mdName;
    }

    /**
     * Returns the mask generation function algorithm name.
     *
     * @return the mask generation function algorithm name
     *
     * @since 1.5
     */
    public String getMGFAlgorithm() {
        return mgfName;
    }

    /**
     * Returns the parameters for the mask generation function.
     *
     * @return the parameters for the mask generation function
     * @since 1.5
     */
    public AlgorithmParameterSpec getMGFParameters() {
        return mgfSpec;
    }

    /**
     * Returns the salt length in bytes.
     *
     * @return the salt length
     */
    public int getSaltLength() {
        return saltLen;
    }

    /**
     * Returns the value for the trailer field.
     *
     * @return the value for the trailer field
     * @since 1.5
     */
    public int getTrailerField() {
        return trailerField;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("MD: " + mdName + "\n")
                .append("MGF: " + mgfSpec + "\n")
                .append("SaltLength: " + saltLen + "\n")
                .append("TrailerField: " + trailerField + "\n");
        return sb.toString();
    }
}
